Research On Polypropylene/Polyethylene/Elastomer Ternary Blending Modification

Polypropylene (PP) is one of the most promising thermoplastic polymer materials today. Compared with other common thermoplastics, PP shows a series of desirable properties, such as relatively good chemical stability, low density and cost, crack resistance, abrasion resistance, excellent insulation, easy processing, dielectric constant, and so on. These properties of PP make it suitable for many applications.However, PP is a non-polar crystalline polymer, large molding shrinkage rate, low surface activity, high brittleness, poor impact resistance particularly at low temperature, which greatly limits its promotion and application. Therefore, it is necessary to toughen polypropylene. At present, the method of mechanical blending is considered as a common method to toughen polypropylene.In this paper, polyolefin thermoplastic elastomers (OBC, EPDM, POE) and styrenic thermoplastic elastomers (SBS, SEBS) were selected as the main toughening agents, adding a certain amount of HDPE to PP for ternary blending toughening. Five systems (OBC, EPDM, POE, SBS, SEBS) of ternary blends were prepared through a twin-screw extruder. The mechanical properties and the melt flow rate of ternary blends were measured. The effect of the content of the two types of thermoplastic elastomers and the ratio mass of PP/HDPE on polypropylene ternary blends were deliberated. Finally, the brittle fracture surface morphology of polypropylene ternary blends was observed by scanning electron microscopy (SEM). The relationship between phase morphology and mechanical properties of ternary blends was preliminary investigated.Results show that:the two types of thermoplastic elastomers (OBC, EPDM, POE, SBS, SEBS) are both effective to toughen PP. For polyolefin thermoplastic elastomers, the toughening effect of POE to PP is best, and EPDM is the second. The processability of OBC is best. For styrenic thermoplastic elastomers, the toughening effect of SEBS is better than that of SBS and the toughness of PP/HDPE/SEBS ternary blends is also higher. However, the flowability of PP/HDPE/SEBS ternary blends is lower than that of PP/HDPE/SBS ternary blends, thus the processability of PP/HDPE/SEBS ternary blends is poor. SEM shows that when the content of POE is20%, a unique HDPE-POE core-shell structure can be observed, which made the interfacial binding force and the toughness of the material superior. There is a good correlation between morphologies and mechanical properties of ternary blends, that is to say, the mechanical properties of the ternary blends are closely related to the particle size of the dispersed phase and how it is dispersed in the matrix.